This invention relates to a table operating device for supporting a table of a machine tool on which a work is mounted and for vertically moving the table and also to an operating method of the table operating device.
In the conventional machine tools, it is commonly the case that a table is fixed to a bed and machining to the work mounted on the table is carried out by moving a tool in various directions with respect to the work.
With such a conventional machine tool, the tool has to be raised above the uppermost surface of the work and lower to below the lowermost surface of the work for machining, thus a stroke of the tool has to be great enough to cover at least a span between the uppermost and the lowermost. In order to set the stroke to at least cover the span, a support member for supporting a main spindle has to be increased in size, resulting in increasing the size of the machine tool as a whole that in turn reflects on the cost. Furthermore, the size increase of such as the support member in its length is likely to lower a rigidity of the support member against the torsional stress thus the negative consequence, lowering the machining precision, will likely result.
In view of the above, a device having a table lifting means for supporting a work mountable table shown in Patent Unexamined Publication No. 8-229758 is considered to be one of the countermeasure. The essential feature of such device is shown in FIG. 11 as a prior part technology to this invention.
In FIG. 11, a conventional table operating device is shown. There is shown a table 100 and a plurality of engageable members 102 extending downwardly from the lower portion of the table 100. On each engageable member 102, there is formed vertically aligned engageable holes 104. Also numeral 106 denotes a bed and a plurality of guide holes 108 for accommodating respective engageable members 102 are formed in the bed 106. An engaging cylinder 110 shown in phantom line is provided to drive its rod member to penetrate through one of the engaging holes in the engageable member 102 to fix the height of the table 100 with respect to the bed 106 when the table 100 is determined to reach a certain height position.
Table lifting means consists of a plurality of screw insertion holes 111, a nut provided in an upper part of each screw hole and a feed screw 114 is inserted through each screw insertion hole and a part of the feed screw is set in mesh with the nut 112. With thus constructed table lifting means, when the feed screw 114 is vertically displaceable by driving a motor 116 to raise and lower the table 100.
With the thus constructed device, it enables to decrease the stroke of the tool to still cover with the machining region between the uppermost and the lowermost of the work mounted on the table due to the relative movement of the work-machining surface relative to the bed. More specifically, the table 100 is adjustable in its height with respect to the floor such that at first the table 100 is positioned at its lowermost position; then the feed screw 114 is driven by the motor to raise the height of the table 100 to the desired position; once the table reaches the desired position, then the engaging cylinder 110 is activated to cause its rod member to penetrate through one of the engageable holes 104 formed on the engageable member 102 to lock th height of the table 100. Once the table 100 is stably supported by the plurality of engageable members 102, then the screws 114 are drive by the motor to lower their positions.
With the above constructed device, an insertion of the cylinder rod 110 into the engageable hole 104 realizes an accurate positioning of the table 100 in the vertical direction. However, attention should be paid to a clearance formed between the outer surface of the engageable member 102 and an inner surface of the guide hole 108. Because of this clearance, the table as a whole can be displaced horizontally by the amount of this clearance, disabling an accurate positioning of the table 100 with respect to the bed. In addition to this drawback, there is a possibility that the table 100 may be displaced during the machining operation as the rigidity of the table in the horizontal direction is relatively low. These drawbacks when combined would seriously affect the precision machining negatively. In view thereof, there certainly exists a room for improvement.